Carbon dioxide has been used for many years in tertiary or enhanced recovery methods in oil fields in order to recover vast amounts of oil which would otherwise stay in the ground.
Since enormous amounts of carbon dioxide are needed to carry out a large carbon dioxide flood in an oil field, the best source for these large amounts of carbon dioxide appears to be the accumulation of carbon dioxide in reservoirs in the earth's formation. Large reservoirs of carbon dioxide have been developed and are being developed in Colorado and Texas, as well as other states.
In the 1940's, certain Colorado wells were developed wherein the production fluid was mainly carbon dioxide. As described in U.S. Pat. No. 2,729,291, the composition of the reservoir fluid was 90.3% CO.sub.2, 4.8% N.sub.2, 2.8% gaseous hydrocarbons, and 2.1% hydrocarbon oil. The phase proportions at wellhead conditions of 72.degree. F. at 1090 psi were about 90% liquid by volume and 10% vapor. The reservoir conditions were at 2350 psi and about 145.degree. F. at a depth of about 5100 feet in one well where the wellhead conditions were about 1050 psi at about 75.degree. F. Thus, while the carbon dioxide was at supercritical conditions within the well, the conditions of the surface were just below the supercritical range. At the surface, the small amount of hydrocarbons was extracted from the carbon dioxide and the latter was then compressed and reinjected into the formation through another well.
In the late 1960's, several gas wells were drilled in Texas which produced natural gas contaminated with 18 to 53% of carbon dioxide. The carbon dioxide, which flowed from the wells as a gas, was separated from the natural gas and subsequently compressed to supercritical carbon dioxide at 2400 psi. The supercritical carbon dioxide was maintained at pressures between 1700 and 2400 psi which it was conveyed through a pipeline. This project was reviewed in an article entitled "Carbon Dioxide Pipeline is Major Engineering Achievement", Pipeline and Gas Journal, November 1971, pp. 44-58.
Recent U.S. Pat. Nos. 4,235,289 and 4,266,607 were issued, which were directed to a method for producing carbon dioxide in a single phase state at the surface from a subterranean formation through a well completed into the formation. The inventors were concerned with maintaining supercritical carbon dioxide produced into the well in a supercritical state throughout its passage up the well to the surface. To this end, a pump or compressor was installed in the supercritical carbon dioxide in the well to boost its pressure in amounts sufficient to overcome friction and hydrostatic head as it was produced up the well to a separator or pipeline at the surface.